Sheet feeders with automatically elevating support trays are well known and are used particularly in high performance commercial copies where high capacity trays are required. For example, in the Xerox 9700 and 1050 machines, the main copy sheet supply tray in both cases is of this automatic elevator type. The operator places a loose stack of sheets on the tray by hand. Then when an appropriate signal is given, e.g. by pressing a control button or closing a cover door, the tray is raised automatically until the top sheet of the stack is brought into operative contact with the feed mechanism. As the sheets are fed from the top of the stack into the processing portion of the copier during use, the height of the stack reduces and as it does so, the tray is elevated automatically to keep the top sheet of the stack in contact with the feed mechanism. To replace or change the stack of copy sheets at any time the support tray is automatically lowered to a base position in response to an appropriate signal, for example when the cover door is opened or when the operator presses an appropriate control button.
In some circumstances it may be desirable to change the stack of copy sheets quite frequently. For example, particularly in a "copy centre" environment, there will be a need to run a whole variety of different throughput materials such as various weights and colors of paper, card stock, pre-punched paper, envelopes, labels, transparencies for overhead projectors, drawing film, and customized pre-printed materials like letter headed paper.
Each time a different throughput material is used the stack has to be physically handled by the operator first as it is inserted into the machine and subsequently as it is removed to make way for a stack of different material. During handling and also during storage the loose stacks of different sheets are vulnerable to contamination and damage which are detrimental to copy quality, high performance machines especially being sensitive to the surface characteristics of the copy sheets, their moisture content, and also to any debris present on the surface of the sheets.
U.S. Pat. No. 4,504,053 to Shiozawa discloses a sheet feed apparatus comprising a fixed base table on which is located a sheet containing bin. A lift is located at the center of the base table and is arranged to rise through an opening therein. The bin, which has a completely open top face, also has an opening in its bottom face through which the lift moves to engage a pallet supporting a stack of sheets within the bin thus raising the stack to a top-sheet feeding apparatus, the bin being locked automatically to the base table when the lift is operational. U.S. Pat. No. 4,248,525 to Sterret demonstrates an example of a top feeding sheet feeder having a support tray movable vertically upward to maintain sheets in operational position. U.S. Pat. No. 4,569,587 to Miyoshi et al. teaches an upwardly biased paper supply cassette which makes sheets available for top feeding. U.S. patent application Nos. 654,706 filed Sept. 27, 1984, and 654,705 filed Sept. 27, 1984 both teach containers for supporting a large number of sheets for feeding.
According to a first aspect of the present invention a sheet feed apparatus having the features specified in the opening paragraph is characterized in that at least one upwardly projecting member is present on the tray in fixed relation therewith, and in that the stack of sheets is provided on the tray in a cartridge having in its bottom face adjacent the support tray an opening permitting entry of said projecting member, the cartridge containing a vertically movable plate for supporting the stack of sheets and extending over the bottom face thereby in operation the projecting member on the elevating tray bears against the underside of the plate so that the plate and the stack are lifted to bring the top-sheet of the stack into operative contact with the feed means.
Preferably the opening in the bottom face is complementary to the projecting member, thereby providing a locating feature for the cartridge on the tray.
In one embodiment the cartridge comprises a generally enclosed rectangular container for holding the stack of sheets, the container having a first opening in the top face for exposing a portion of the top sheet to permit the sheet feed means to engage said top sheet, a second opening in a side face and extending to the top edge of said side face, through which second opening sheets can be fed from the top of the stack, and a third opening in the bottom face arranged to permit entry of the projecting member, whereby in operation the projecting member(s) of the elevating tray bears against the underside of the plate so that the plate and the stack of sheets supported thereon are lifted within the container to bring the top sheet of the stack into contact with the top face of the container thereby raising the container until the top sheet of the stack is brought into operative contact with the sheet feed means.
According to another aspect of the present invention there is provided a cartridge for use in the sheet feed apparatus in accordance with the first aspect, comprising a generally enclosed rectangular container for holding a stack of sheets to be fed, the container having a first opening in the top face for exposing a portion of the top sheet of the stack to permit the sheet feed means to engage the top sheet when the cartridge is in use in the sheet feed apparatus, a second opening in a side face, through which second opening sheets can be fed out from the top of the stack when the cartridge is in use in the sheet feed apparatus, and a third opening in the bottom face arranged to permit entry of the projecting member(s) when the cartridge is in use in the sheet feed apparatus, the cartridge further comprising a vertically movable plate for supporting the stack of sheets, said plate being disposed within the container adjacent the bottom face and extending over the third opening such that when the cartridge is in use in the sheet feed apparatus the underside of said plate is engaged by said projecting member(s).
The use of this cartridge to hold the stack of sheets not only simplifies change over of throughput material, but also means that the individual sheets are less likely to be damaged or contaminated because the operator does not actually touch the stack when it is being loaded into and out of the sheet feed apparatus. The cartridge also provides a convenient means of storing either full or part-used stacks of sheets, its generally enclosed construction helping to protect the contents from the environment without the need for a separate protective storage box.
According to yet a further aspect of the invention there is provided an adaptor for converting a sheet feed apparatus having an automatically elevating stack support tray to operate with a stack of sheets provided in a cartridge in accordance with the previous aspect, the adaptor comprising at least one projecting member, and means for attaching the projecting member(s) to the upper side of the support tray.
With this adaptor a conventional sheet feed apparatus having an automatically elevating stack support tray can be converted quickly and easily to operate with a cartridge instead of a loose stack of sheets.